The present invention relates to multi-station sand mold making apparatus for producing sand molds for foundry use, and more particularly to a strike off apparatus for automatically leveling and compacting sand in mold boxes of varying heights carried in succession along a pathway.
Multi-station sand mold making apparatus have been known heretofore. It is desirable that such apparatus be capable of simultaneously producing the cope (upper half) and drag (lower half) portions of a composite sand mold, the two portions being complete and assembled upon each other and ready for the molten metal pouring operation at the time they leave the apparatus. Typically, a plurality of mold boxes, each containing a mold pattern, are circulated around a closed pathway through a succession of stations at which different mold making operations are performed.
At one station a predetermined amount of sand containing a binder and a catalyst is poured into an open-top mold box. The mold box is simultaneously vibrated to eliminate voids and produce some compaction of the sand. The amount of sand which is poured into the mold box is sufficient to form a mound which extends above the upper edges of the box.
At a succeeding strike off station the sand is distributed, leveled, and slightly compacted before the binder hardens. This may be done by hand tamping, by using a ramming apparatus, by using revolving rollers, or by some other known technique. By distributing it is meant that the mound of sand is spread more or less evenly throughout the mold box. By leveling it is meant that a smooth, horizontal upper surface is imparted to the sand which usually coincides with the upper edges of the mold box. By compacting it is meant that the space between the granules of sand is reduced.
When the apparatus of the present invention is utilized at this station, voids or gaps adjacent the pattern are eliminated. This ensures a more precisely defined casting. Also, the sand is compacted to a uniform density. Without such a uniform density, regions of the completed, hardened composite sand mold can prematurely crumble or fracture when the mold is filled with molten metal. This ruins the casting. When the sand is compacted with the apparatus of the invention, the cope and drag portions produced have smooth horizontal parting surfaces which mate when the cope and drag portions are joined to form a composite sand mold. Molten metal cannot seep between the cope and drag portions which would otherwise have to be removed by machining after hardening. Another important advantage relates to the fact that a drag portion eventually rests on its surface which has been leveled and compacted. Since this surface is smooth and horizontal, the composite sand mold is stable, i.e. it does not tilt or rock. If the composite sand mold tilts or rocks while molten metal is being poured into it, the metal can miss the pouring hole in the mold.
U.S. Pat. No. 400,893 discloses an apparatus for leveling and compacting sand in an open-top mold box. The box is conveyed underneath a pair of rollers which extend transversely of the direction of travel of the mold box. The first roller which contacts the sand is positioned slightly higher than the second roller. The first roller levels the sand before it is further leveled and compacted by the second roller. The surface of the first roller is made of rubber or other resilient material to prevent hard chunks from interfering with the leveling and compacting. Leveler blades are mounted after each roller. Mechanisms are provided for independently adjusting the height of the rollers. The axles of the rollers are mounted in journal boxes which have spring mechanisms but it is not clear whether the rollers are biased downwardly against the sand. Gear mechanisms rotate the rollers in the same direction. The rollers could be made to rotate against the direction of travel of the mold box, although this is not clear from the patent.
U.S. Pat. No. 1,759,728 discloses a similar apparatus which employs a pair of rollers for leveling and compacting sand in an open-top mold box. The first roller is positioned higher than the second roller whose lower periphery is at the same height as the top edges of the mold box. The rollers rotate so that their lower peripheries travel in the same direction as the direction of travel of the mold box passing thereunder. The axle of the first roller is journaled in two bearings whose height can be vertically adjusted. The axle of the second roller is pivotally mounted on the axle of the first roller, however, the height of the second roller is apparently fixed during the leveling and compacting operation by adjustable rods.
Neither of the aforementioned patented apparatus is adapted for automatically leveling and compacting sand in mold boxes of varying heights carried in succession along a pathway. The rollers of each must be manually adjusted to a precise height if a mold box is to be run thereunder which has a different height than the immediately preceding mold box.